(a) Field of the Invention
The present invention relates to a method of controlling an engine stop position in a hybrid electric vehicle. More particularly, the present invention relates to a method of controlling a crankshaft position when an engine is to be stopped in a hybrid electric vehicle so as to minimize torque ripple and vibrations generated during intake, compression and expansion strokes when the engine starts up.
(b) Background Art
In general, a hybrid electric vehicle (HEV) utilized both an engine and a motor driven by a battery power source. Typical HEVs are either parallel type or series type, and include an engine control unit (ECU); a motor control unit (MCU); a transmission control unit (TCU); a battery management system (BMS); a full auto temperature controller (FATC), which controls room temperature; and the like.
Such controllers are linked with each other through a high-speed CAN communication line (e.g. 500 kbps), which is controlled by a hybrid control unit (HCU). Cooperative control is performed between the HCU, acting as the superior controller, and the other, subordinate controllers.
The HCU exchanges information with the subordinate controllers through the CAN communication and controls the subordinate controllers. That is, the HCU receives information on engine torque, engine speed, start key, throttle/coolant temperature, and on the like from the ECU. Moreover, the HCU transmits a fuel injection command signal, an engine stop command signal, a fuel injection cut-off command signal, and information on electric motor start-up, idle stop, and the like, to the ECU.
Moreover, the HCU substantially controls the operation of the electric motor through the MCU. In this case, the MCU controls drive torque and speed of the electric motor according to the control signals transmitted from the HCU, thus maintaining the driving performance.
An integrated starter generator (ISG) functions as both a starter motor and a generator for charging the battery.
The ISG is connected to the engine by a belt to rotate synchronously with the engine. Accordingly, the rotational speed of the ISG is determined in accordance with a pulley ratio from the engine speed. Moreover, the ISG performs the functions of starting the engine during the engine start-up, generating high power for charging the battery using the rotational force of the engine while driving, and stopping the engine in a state where the fuel supplied to the engine is cut-off when the engine is to be turned off.
Piston and crankshaft stop positions (engine stop position) change every time the engine is stopped. Accordingly, if the ISG supplies a predetermined starting torque to the engine to restart the engine, torque ripple and vibration are generated from the engine according to the variation of the engine stop position.
Accordingly, in order to prevent engine vibration, it is desirable to control the engine stop position, i.e. the piston and crankshaft positions, regularly at all times when the engine is to be stopped.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.